1. Field of the Invention
The present invention relates to a power transmission device of an automobile, and in particular relates to a power takeoff unit for distributing torque from first axles to second axles in a four-wheel drive vehicle for example.
2. Description of the Related Art
In a front-wheel drive vehicle for example, an engine installed on the front of a vehicle body generates torque and a transmission receives and distributes the torque to left and right front wheels via a differential. A four-wheel drive vehicle in general employs a power takeoff unit (PTU), in combination with such a transmission, for distributing part of the torque to rear wheels.
A PTU converts torque about an input shaft extending in a lateral direction relative to a vehicle body into torque about an output shaft extending in a lengthwise direction. The output shaft is drivingly coupled with a propeller shaft through which the torque is transmitted to the rear wheels.
To realize part-time four-wheel driving, a device for controllably permitting/interrupting torque transmission is often used on the transmission path of the torque. It is beneficial to interrupt torque transmission at a point upstream of a heavy propeller shaft in light of reduction of energy consumption. Thus the device for permitting/interrupting torque transmission is preferably installed in the PTU. This may lead to size-grow of the PTU.
As a PTU is in general disposed in parallel with a transmission, its output shaft inevitably laterally deviates (offsets) from a center of a vehicle body, and therefore a propeller shaft coupled therewith accordingly makes an offset. It is preferable that loads and forces acting on the vehicle body are symmetric. Therefore, the offset of the propeller shaft is unfavorable because the propeller shaft is relatively heavy and elongated in the lengthwise direction of the vehicle body although it is given torque. More specifically, the offset of the output shaft of the PTU as well as the propeller shaft has been a long-felt but unresolved technical problem.
Japanese Patent Applications Laid-open No. 2009-269605 and No. 2009-292307 disclose related arts.